There is disclosed a two-chamber-type side airbag in which an airbag is divided by a partitioning wall into a first airbag portion positioned at the upper side and a second airbag portion positioned at the lower side, and the partitioning wall is structured by a portion of a cover of the second airbag portion, and the side airbag has, at the rear region of the airbag, a holder (diffuser) that is made of cloth and is for housing a gas generating device and spans between the first airbag portion and the second airbag portion (see Patent Document 1).
Further, there is disclosed a structure in which the interior of an airbag for a side collision is divided by a seam into an upper chamber and a lower chamber, and a communicating portion that communicates the upper chamber and the lower chamber is formed between the seam and the rear edge of the airbag, and a tube-shaped check valve is provided at the communicating portion, and a gas generator is disposed within the check valve, and, due to the flowing-out of gas from the lower chamber to the upper chamber being impeded by the check valve, the gas pressure within the lower chamber is maintained high as is even if the body of a passenger hits the lower chamber (see Patent Document 2).